The invention relates to pulsed-DC arc welding, and more particularly to techniques of this type in which a welding current having a cyclic pulse component superimposed on a steady DC component, is applied to a consumable welding electrode in contact with a work to be welded in a protective medium.
Existing pulsed-arc systems of this type suffer from several drawbacks. In particular, unless an inert gas atmosphere (e.g. principally argon) is maintained, it is difficult in existing systems to control the rate and characteristic of the transfer of drops of molten metal from the welding electrode to the work during the formation of a weld seam. Additionally, in the absence of such an inert atmosphere (and in particular in the presence of active gases such as carbon dioxide), the danger of back-blowing of the molten metal is always present.
In addition to exhibiting a low efficiency in the presence of active media such as carbon dioxide, such existing pulsed-arc welding processes employ, for the generation of the pulse component of the arc, either phase-pulsed thyristor control or thyristor-instrumented interruption switches interposed between a DC source and the welding electrode. The first of these techniques is subject to severe frequency limitations imposed by the frequency of the AC mains, while the latter technique is subject to a relatively low peak amplitude level of the pulses.